It is often desirable to exchange digital information between digital machines. If such machines are separated by any significant geographic distance, it has heretofore been necessary to either purchase or lease a dedicated transmission facility between such machines, or to arrange a temporary connection between such machines by means of common carrier, switched transmission facilities. Since it is the nature of digital machines to require large amounts of digital channel capacity, but only for brief periods and only occasionally, the heretofore available facilities described above have proven very inefficient for this use. Dedicated transmission facilities, for example, remain unused the vast majority of the time. Switched, common carrier facilities tend to be restricted in bandwidth to voice frequencies and are otherwise unsuitable for digital, as contrasted with analog, transmission.
A further problem with switched facilities is the fact that it often takes more time to set up the transmission path than is required for the entire transmission of data. The telephone network requires real time transmission in the sense that signals must be delivered substantially at the same time they are generated. It therefore is standard procedure to set up the communication path in its entirety before any signals are transmitted. As a result, centralized switching has been used in the telephone plant. Digital transmission of data, on the other hand, need not be done in real time and hence it is wasteful to set up an entire connection prior to transmission. These facts tend to make presently available interconnection facilities uneconomical for intermachine digital communications.
It is an object of the present invention to provide improved digital transmission facilities for communication between digital machines.
It is a more specific object of the present invention to provide the efficiency and economy of digital transmission over large geographical areas.
It is another object of this invention to provide a national communication network for digital transmission between digital machines.